This invention relates to a braking hydraulic pressure control valve used in a dual-circuit brake system wherein braking hydraulic pressure generated in a master cylinder is delivered to each of the left-and right rear-wheel-brakes of a vehicle through a pair of mutually independent conduit circuits.
It is commonly practiced in vehicles that a master cylinder is connected to each wheel cylinder disposed on the left-and right rear wheels by a pair of mutually independent conduit circuits for delivering the braking hydraulic pressure generated in the master cylinder due to operation of a brake operation member to the wheel cylinders independently from each other.
The applicant of this invention recently developed a control valve for controlling the braking hydraulic pressure delivered to the left-and right rear wheels in a dual-circuit brake system, wherein valve pistons of a pair of proportioning valves were parallelly disposed in a housing and one biasing device was shared by both valve pistons. In this control valve, the biasing device comprises (a) a guide rod swingably retained at one end thereof with a pivot pin, at a position middle of the pair of valve pistons, (b) a transmission or sliding member provided with a cylindrical portion slidably fitted on the guide rod and an action portion abuttable on rear ends of the valve pistons, (c) a compression coil spring anchored between the transmission member and the guide rod for constantly imparting biasing force to the rear ends of the valve pistons, and (d) a stopper projection extended from one end of the guide rod on the side thereof retained by the pivot pin for being fitted with a predetermined clearance into a stopper hole formed in parallel with the valve pistons within the housing so as to limit the swinging of the guide rod within a minute angular range from a straight center line passing the axis of the pivot pin and parallel to the axes of the valve pistons.
In this braking hydraulic pressure control valve, resilient force of one spring is equally distributed by a transmission member to a pair of valve pistons and an ununiformity of operational stroke between the pair of the valve pistons owing to errors in manufacturing can be absorbed by the swinging of a minute angle of the transmission member and the guide rod. And when one of the pair of independent conduit circuits is damaged, the transmission member is straight linearly moved on a retaining member which has been blocked of swinging exceeding a predetermined range. It causes the valve piston receiving the hydraulic pressure from the normal conduit circuit to compress the coil spring by itself, so the hydraulic pressure in the normal conduit circuit advantageously becomes two times as high as when the both conduit circuits are normal before the hydraulic pressure control begins to take place. Besides, the guide rod may be attached to the housing or a member secured thereto with a simple pivot pin and the transmission member is allowed to be slidably fitted on the outside of the guide rod of bar shape, which makes the manufacturing of the two members quite easy.